In our prior application Ser. No. 381,498 referenced above, there are disclosed fibrous ceramic insulation materials formed by dispersing a suspension of ceramic fibers over a form-defining surface, partially drying the fibers to form a mat, solidifying the mat by first soaking it with a sol-gel ceramic precursor then setting and curing the sol-gel precursor. The present invention is directed to an improvement over that fibrous ceramic, which has improved internal strength, readily tailorable dielectric properties, greater achievable thicknesses as compared to the fiber/microparticle ceramic of our prior applications, and the ability to provide a strong attachment means on the ceramic by overhanging the ceramic cloth.
The present invention also improves on the fiber/microparticle ceramic of our application, filed on an even date herewith, referenced above, which is made from a mixture of ceramic fibers and microparticles by setting the mixture using a sol-gel.
The improvement is provided by using ceramic reinforcement cloth (which may be in tow form), bound within the mat by sol-gel glass bonds. We have found that the rigidized fibrous mats made in accordance with our prior applications consist of fibers which are randomly tangled, most of which are oriented in the x-y plane (the z-axis being aligned with the thickness of the mat). When bound with the sol-gel binder, a fibrous three dimensional network provides a material, with a porosity of about 90-95%. According to our application filed on an even date herewith, the voids between the ceramic fibers may be filled by microballoons and/or diatoms, thus further rigidizing the structure and improving the isotropic structure characteristics of the fibrous material. According to the present invention, the rigidized fibrous mat is strengthened by one or more continuous ceramic reinforcement cloths which are bound by sol-gel glass bonds between layers of the rigidized fiber.
The ceramic composite according to the present invention is characterized not only by improved internal strength of the fibrous ceramic by use of the reinforcement cloth, but also greater thicknesses of the fibrous ceramic may be achieved by virtue of this reinforcement. In addition, the dielectric properties of the ceramic can be tailored by the selected placement of, and by the type of, ceramic cloth.
Another improvement provided by the present invention is that ceramic cloths having larger areas than the fibrous mat may be used, thereby providing peripheral flaps of ceramic cloth extending beyond the fibrous mat which serve as a means for attachment of the fibrous ceramics to one other or to a support to make, for example, insulation plates for furnaces and engines.